Recording 2.0

Mixxx currently supports simple recording to a file. We should really expand on this feature and make recording a first-class feature in the library.

I propose we:
1) Make a 'Recordings' or 'My Mixes' section of the library.
2) You start and stop recordings from this section of the library. No more context menu.
3) The files are managed by Mixxx and stored in a 'My Mixes' folder in your computers' My Music folder, or a custom location.
4) You can see your recordings, and the dates they were made, in the library feature.

Having Recording as a first-class library feature puts us in a prime spot to add more fancy features related to this.